2muchhp
VIP Member
I am looking at the piston specs and see that the number is 2.7143-2.7144.To me this number seems a bit unrealistic .0001(one tenth on the diameter/ 50millionths per side? I checked the pistons from my srx with 7500 miles and they check 2.7106 and the pistons from my Viper with 2500 miles check within a couple tenths of this number. are all 6 of these pistons really junk? Checking tolerances within one tenth wow who has a temp controlled room I can use.
I just hate to scrap good Yamaha pistons if not needed. I am doing the viper to srx head swap and just checking everything out before assembly. Any thoughts would be appreciated.
I just hate to scrap good Yamaha pistons if not needed. I am doing the viper to srx head swap and just checking everything out before assembly. Any thoughts would be appreciated.
well your pistons are worn .004", the next question would be how much skirt to wall clearance do you have in the cylinder? that spec is more important in my opinion.
You do have the option to have the pistons coated at swain tech to bring the skirt to wall clearance into the right range. I do this often for guys and it works very,very well. The yamaha pistons are very good units and last a long time, this extends thier life by many more miles and makes it work even better as the skirts are more slippery with the pc9 on them.
You do have the option to have the pistons coated at swain tech to bring the skirt to wall clearance into the right range. I do this often for guys and it works very,very well. The yamaha pistons are very good units and last a long time, this extends thier life by many more miles and makes it work even better as the skirts are more slippery with the pc9 on them.
2muchhp
VIP Member
Right, which by Yamaha standards is way out of spec. I haven't got to checking the wall clearance yet,Ill go check it out brb in 10.
2muchhp
VIP Member
I checked one cylinder and its 2.7160, so .0054 total or .0027 per side. How much really is to much?
that being said if my pistons were at max spec and seeing my cylinder size I would have .0008 per side
seems pretty tight.
that being said if my pistons were at max spec and seeing my cylinder size I would have .0008 per side
seems pretty tight.
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.0054"...that would be loose as a goose.... I use wisecos at .0035-.004". The yamaha piston expands alot less then the wisecos and can run a tighter skirt to wall(thats the advantage).
Will it run as is??... sure, but its not gonna give you good stability and the rings will wear quicker this time due to the piston can rock back and forth in the bore more, the rings try to stabilize the piston and can only do so for so long.
I would personally send out the pistons and have them coated to tighten it back up some.
.003-.0032" is about my personal limit then I coat the pistons.
(not meant to you specifically) but this is precisely why I tell people these things need rings replaced at normal interval;s, sure, they will continue to keep running but they wear the skirts and lose power gradually overtime that most people dont notice it. Youll see all over this site how great guys sleds run with 10,000-20,000 miles never touched but they have no idea how much power its down at that point. After awhile the piston will get so sloppy the skirts break off and then it gets real ugly fast........
cheap quality oil contribututes to this as well, seen some worn with only a couple thousand miles like your other one.
Will it run as is??... sure, but its not gonna give you good stability and the rings will wear quicker this time due to the piston can rock back and forth in the bore more, the rings try to stabilize the piston and can only do so for so long.
I would personally send out the pistons and have them coated to tighten it back up some.
.003-.0032" is about my personal limit then I coat the pistons.
(not meant to you specifically) but this is precisely why I tell people these things need rings replaced at normal interval;s, sure, they will continue to keep running but they wear the skirts and lose power gradually overtime that most people dont notice it. Youll see all over this site how great guys sleds run with 10,000-20,000 miles never touched but they have no idea how much power its down at that point. After awhile the piston will get so sloppy the skirts break off and then it gets real ugly fast........
cheap quality oil contribututes to this as well, seen some worn with only a couple thousand miles like your other one.
1 other thing to mention, you took and average on the cylinder check right? seeing how the skirts never reach the top, I spend more time checking the middle and bottom of the cylinder, youll find it will be slightly snugger if you measeure that then at the top above the ports to the top, the rings put the most wear at that area(top), so check with a couple measurements at center and lower some and see what you come up with.
I hope I didnt rain on your parade with previous post, nobody likes to spend more money,me included....lol
2muchhp
VIP Member
That dimension is the largest number I found from mid to bottom of cylinder,it didn't vary much 2-3tenths or so. No rain here I hope for good answers that
make sense, not answers that I would like to hear. I don't like being towed nor do I like stuff that is not tuned to perfection,however I am not loaded with cash
so like most have to find a happy-medium. thanks a bunch for you input. Is the coating cheaper than new pistons?
Can I just call swain tech and they will hook me up with sending my pistons out etc. Is it a standard thickness they coat or do I need to tell them the specs?
I could kick myself for waiting till now to start this project,I bought the Viper late last season (rode it in the back yard once)after wrecking my srx,knew I wanted to use the parts off the srx on the viper but didn't start anything until after it snowed.
make sense, not answers that I would like to hear. I don't like being towed nor do I like stuff that is not tuned to perfection,however I am not loaded with cash
so like most have to find a happy-medium. thanks a bunch for you input. Is the coating cheaper than new pistons?
Can I just call swain tech and they will hook me up with sending my pistons out etc. Is it a standard thickness they coat or do I need to tell them the specs?
I could kick myself for waiting till now to start this project,I bought the Viper late last season (rode it in the back yard once)after wrecking my srx,knew I wanted to use the parts off the srx on the viper but didn't start anything until after it snowed.
go to swain tech website and download order form, then specify pc9 heavy build. They cant hold a tolerance on high build so i just measure them when they come back and then polish with wet sandpaper to get to where i need to be. its very easy to work with.
its way cheaper then new pistons!
all the prices and stuff are on thier website.
its way cheaper then new pistons!
all the prices and stuff are on thier website.
2muchhp
VIP Member
I checked it out it looks real good .You ever had the tops coated? I know the Yamaha pistons good,is it worth it?
I dont personally get the tops done, I didnt care much for it as it made them very hard to read, the wash marks and such dont show up on them as the coating makes them slick. I am sure it helps for heat reflection off the domes but its alot harder to tune so I just do the skirts.
2muchhp
VIP Member
Yea I wondered about reading wash.When I get them back what would you recommend lapping the clearance to.
2muchhp
VIP Member
Yea I wondered about reading wash.When I get them back what would you recommend lapping the clearance to,anything different than Yamaha specs.
wet sand off the least amount possible...lol!! measure them first as shipped back and adjust to anywhere from .0025"-.0032" skirt to wall is good to go.
p.s. I bead blast mine before I send them, if not possible for you to do be sure to clean them good with brake clean and a scour pad or equal, this way you know the coating bites in good. That stuff stays on there a long time(1000's of miles) if prepped right!
2muchhp
VIP Member
No bead blaster,just a hand held sand blaster.
thanks again for the help
thanks again for the help
Since its close to X-mas I will do you a gift...lol, make out your order for your pistons with swaintech and then send them to me first, I will beadblast them for you and forward your order to swain, I am on the way so it wont delay your time much.
Not big deal for me about 10mins of work involved, this way i know your gonna get a good job back. I look at it as paying it forward to someone.
pm me if you want me to do it for you. Up to you, I try to help everyone out if I can. thanx
Not big deal for me about 10mins of work involved, this way i know your gonna get a good job back. I look at it as paying it forward to someone.
pm me if you want me to do it for you. Up to you, I try to help everyone out if I can. thanx
2muchhp
VIP Member
Thanks for offering I really wasnt expecting that but I hate to wear out my welcome. prepping the piston I should be ok with.I ordered a racelogic port template a couple of days ago,I may need to pick you brain on that a bit also
2muchhp
VIP Member
Received my pistons back from Swain Coatings yesterday...very nice job. Thanks mrviper for the "paying forward help".
Now if I can only get enough heat in my garage to keep form freezing to death while getting this back together.
not a problem.
pm me your address if you want some xxx jerky,keep a cold beer with it,youll need it...lol
pm me your address if you want some xxx jerky,keep a cold beer with it,youll need it...lol